1. Field of the Invention
The present invention relates in general to methods for connection of precast concrete units in construction work, for example, connection of beam to beam, wall to wall, wall to slab, slab to slab or etc., and more particularly to wet connection methods for connecting the precast concrete units to each other in which concrete placed in the connection part between the units is electrically heated, thereby shortening the curing period and the term of work.
2. Description of the Prior Art
In recent, precast concrete units for the construction of buildings or other structures, particularly for the beams, columns, walls and slabs thereof, are efficiently utilized to simplify the site work and, in this respect, to shorten the term of works. Also, the precast concrete units generally have a sufficient strength for attaining the structural strength required to withstand handling loads and loads imposed by the structure. In order to carry out the construction of structures using such precast concrete units, the units are connected to each other. Conventionally, the methods for connection of the precast concrete units are classified into two types, that is, a dry connection method and a wet connection method.
In the typical dry connection method, a short I-beam or steel plate is partially embedded in each end of the precast concrete units in order to be bolted or welded to each other. However, this type of method has a problem in that it is relatively expensive. Furthermore, the exposed part of I-beam or steel plate used in this connection must be covered with concrete after completion of connection work for the protection against fire and corrosion, thereby inducing a problem of complex work process.
Meanwhile, FIGS. 21 and 22 show an embodiment of a typical wet connection method for beams and columns and a bending moment diagram of the frame after completion of connection, respectively. As shown in FIG. 21, in the typical wet connection method, concrete is placed into the connection parts 303, at which the precast concrete beams and columns are connected, respectively, then cured at the site temperature and this causes the next step of work not to start until the concrete placed in the connection parts 303 is sufficiently cured. In this respect, a problem of this typical wet connection method is resided in a fact that the term of work is inevitably lengthened. On the other hand, the precast concrete beams 301 are typically supported by columns 302 so that the connection part should be located on the columns, where the maximum bending moment of the frame tabes place. In result, another problem of this typical wet connection method is resided in a fact that cracks are apt to be generated at the connection part 303 and this results in a structural defect.
Steam or hot air can be used in order to shorten the curing period of the concrete-placed in the connection parts 303. However, this type of curing method has a problem in that it needs a complex and heavy equipment and the steam or the hot air can not efficiently heat all over the inside of the concrete applied to the connection parts 303, thus causing this curing method to be practically scarcely used.
Accordingly, if briefly described, the wet connection method has an advantage in that it is less expensive, from the viewpoint of the construction cost, than the dry connection method, while it inevitably has a disadvantage of the longer term of work caused by the longer curing period than the dry connection method. In this respect, it has been required to provide a noble precast concrete unit connection method which can cure the concrete placed in the connection parts in a shorter time than the known wet connection method, thus shortening the term of work.